The field of the invention relates to utilities and the invention relates more specifically to underground structures used in conjunction with electrical utility structures.
Electrical transmission lines are often carried below ground level in large conduits and in order to service such conduits, openings must be provided below the ground level and such openings, for years, have been covered with heavy metal covers referred to as manhole covers. Manhole covers are supported by cast iron frames held at the ground surface level, and such frames invariably provide for a gasket to reduce the likelihood that water, or more seriously, chemicals, diesel oil and other liquids which could interfere with electrical transmission leak passed the manhole cover into the structure below. Furthermore, the presence of the gasket reduces the rattling noise between the cast iron cover and the machined surface of the frame upon which this cover rests.
In the past, O-rings have been placed in generally rectangular grooves formed in the cast iron frame. Unfortunately, when the manhole cover is removed for use, it is quite common that the O-ring is dislodged when the cover is replaced in the cast iron frame. This happens, in part, because of the propensity of an O-ring to turn and ride out of a groove. Naturally, the manhole cover is very heavy with a typical 30-inch manhole cover weighing approximately 290 pounds. Thus, in practice, it is slid onto the frame, and the edge of the manhole cover can easily touch the gasket and dislodge it. Once dislodged, the seal is ineffective and large amounts of water, or other chemicals, can enter the underground structure.
There is, thus, a need for an improved gasket which will not become dislodged when the manhole cover is replaced onto its cast iron frame.